Acrylonitrile extraction process



A n 18, 1961 w. G. JoHNsoN 2,980,726

AcRYLoNTRLE ExTRAcToN PROCESS F11ed Dec. 29 1958 NVENTR WILLIAM G,jOHNSON ATTORNEY Unito Tho pfesent invention felateS to a pfoceSS foftreating the pToduct StfeaTn ffon1 a feactof in vvhich aor lonitTile iSynthesized. Mofe pafticulafly, thiS inventlon TelateS to o proceSS foftTeating the pfoduct Sfream so as to fecoveT acTyloniffile and topfovide a fecyc1o gas stfeam.

In carrying out the Inanufacture of acfylonitTne by the Teaction of11ftfic oXide and pTopylene in the pfesence of a dehydrogenationcatalyst aS disclosed in IJ.S. Patent Z,736,739, InaXiInnIn yieldS andconvefsionS afe obtained When a lafge eXceSS of pfopylene iS USed in thepfocess. EoonoInic conSidefations Tnake desiTable the uso of thecon1Inercially available propylene Which contains about 1S) by voluIneof ofopane as the hydfocaTbon feed, and the uSe of the prodoct StTeaInf1 Om an anlInonfa oXidation unft vvhich contains aboI1t 15% by volun1eof nitfic oXide, fhe fenainder being pfiInarily nitTogen, as the nitricoxide feed. The offga S from the acTylonitTile synthesiS thuS containS,in addition to acTy1onitri1e a11 of the nitfogen, a11 of the opane, andthe onfeacted por tion of the pfopyleoe in the ofiginalfoed.

SiTnple TeTfloval of the aofylonitfile and discafd of fhe feTnaindef ofthe ofgaS is not econoInicallyv feaSible 1n view of the high content ofpropylene TeTIlainihg i 1 fhe offgas. Alternative1y, diTect fecyole ofthe gaS StfeaIn afteT the feInoval of the acTylonitfile is notfeaSibloeithe State Paten .ene,

fCe

fion is dependent on the pTopef choice of solvent, The solvent to beadded n111St not forn1 an aZeotfope With any of tho coInponents to beSeparated, and it InI1St have a higher boiling point than niffogen,pfopane, of pfopy1 The solvent Inust have a different effect upon thopaTtial preSSufes of pTopane and pTopylene in Solution.

bocanso of the incTeaSed ropoftion of niffogen andpTopane SI1ch recyclevvould intfoduoe to the systeTI1. obviously, the n1ost desiTable TecycleSffean1 Wou1(1 be one containing only pfopylene and pfopane ineSSentla1ly the SaTne pfopoftionS as in the origina1 hydfocarbon feed.T1I1s a procedure is needed toTeInove the acTylo niffile, the nitrogen,and a poftion of the pfopane fTo n v the Teactof offgaS.

The acrylonitrile can be ren1oved frofn the off-gas by Simply Cooling tocondenSe the acfylonitfile, of the nif ogen oan easily be SepaTafedfroIn the off-gas by abSorbing the pfopane, pfopy1ene, and acTlyonitrilein a sualole solvent Ren1oval of a portion of the pfopane ffofn theoff-gas vvithout siTnlIltaneoUS Temoval of pTopyleno, hovvever, is an1ofe coTnplex InattoT. The Ten1ova1 of a poTtion of the propane flomthe offgas by ordinaTy fractional dfSti11a tion iS eXceedingly diHic1 ltand highly iInpfactical -becauSe of -the closely Si1T1ilarvapofpTeSSureS of pfop ane r and oropylene. IIovevef, a vapof1iqoidphaSe SepaTation of p ropylene from pTopane iS possible by eXtfactiyedistillation of tl1e n1ixtnTe in the pfesence of a Telatively,

higheT-boiling selective solvent vvhich ill increase the Spfead in thevapof pfeSSUTeS, and fhus in felative vo1atlitieS of the propylene andpTopane. The vapor fTaction viH be enriched in the component Shovvingthe leSS dovia tion froIn Raou1t,S 1aw of ideal solotionS, and the botfonS of liqUid fraction vVill conSist of tho added soIvent enfiched inthe component Showing the gfeatef deviation ffom Raoult,S law.

TT1e e1ectiveneSS of a Sepafation by extfactive diSti1a,

an(1 ro ane are 11ashed fron1 the solvenf.

, To fulnH the )ToSent fequifoInentS, the extfactive disti1 lationSolvent TnnSt pern1it the deSiTed degTee of Separation of pfopane ffon1the acTylonitTile feactof off-gaS, n!USt absorb eSSentially all theacrylonitTile pfeSent, and InuSt peTIT1it the Separation of eSSentiallyal1 the nitfogen.

Accofdingly, it iS an obiect of the pfeSent invenfion to pfovide anTethod foT reducing the pfopane content in an acry1onitfile TeaotofoffgaS contaioing pTopane pfopy1ene, nitTogen, .and acflyonitrile. It iSanofhor object of this invention to Tecover eSSentially aH of thoaofylonitfi1e ffon1 an acry1onitfile feacfoT ogaS containing pfopane,pfopylene, nitfogen, and acfylonitfile. It iS a fofthef obioct of thiSinvention to pTo vide a n1ethod foT the separafion of esSentiaHy a11 fhenitfogen fTom an acTylonitfile feactor off-gas oontaining pfopane, fopy1ene, nitfogen, and aoTylonitTile. It is a Stfll further ob ject of thisinvention to pfovide a Tnethod Whefein the Tedootion of the pfopanecontent, Tecovefy of tho acrylonitfile, and Sepafafion of the nitfogenffoIn an aofy1o nitTile feactof v offgaS r oontaining Pfopane,propylene, nitfogen, and acTylonitfile afe caTfied ontoiTnultapeously.0theT obiectS Wi11 becoIne appaTent as the invention iS mofe foHydeScfibed.

I have found that the fofegoing obectS aTe achieved vvhen I introduce anacfyIonitfile feactof ogaS contain ing pfo ano, pTopylene, oitfogon, andacfylonitfile info the lower poTon of a rectiEcation towel and intfoducebenzonitfile into the upper portion of .the tovver to pef^ n1it thebenzonitlile to oontact.the propane-pfopylenenitfogen-acfylonitTileStfeaIn in countefourfent Te1atioI1 Ship, the quantities of ingTedfentSand the conditions of opofation being SUch that esSentiaHy alf of thenitfogen and a poftion of the pTo Jane Wi11 be vvithdrawn as vapof.

A How diagfaIT for a pfoceSS usiog fhe solvent of thiS invention iSShown in Figofo` 1. The dTaWing iS illllstfative only and not to beconstrued as liIniting the inventrayS, Sieve platoS, bubble-oao p1ates,of packing, to a height coffesponding to a nUo1bef of theofotioal platesas oalculated by o n1ethod vve11-knovvn in the aft, e.g.,

- heat and ITlaterial balanceS on each plate, corrected by theeITlpificaHy detefInined p1afe efcienoy. vapof onfiohed fn propane andcontaining eSSentially all of the nitrogen is feInoved ovefhead throughline 5. .1 li(11idfraction conlpTising the solvent containingessentially aH of the acfy1onitrile, the pfopylene, and thopTopane notrenloved aS vapof is vvithdfavn fron1 tovZer Z throngh line 6 andintroduced into oolun1I1 7 vvheTe the pfopylene The propyl ene andpTopano are recovefed through line 8 and fe cyoled to the acTy1onitfilefeaotor. The propane and pfopylenefTee Solvent containing acrylonitIileis With dTaWn from colomn 7 through line and intToduced intodiStillation colun1n 10 vvhefe the acTylonitfile fS fraction allydistilled froIT1 the solvent. The acfylonitrile is fe- Inoved fromcolumn 10 thTough line 11 and Sent to a fenef. throngh line 12 andTecycled to Tectification tovvefZ.

The fonowing exan1pleS illustfafe a Tnethod of carry- The Solvent isdisoharged fron1 oolllIfIn 1f} 3. A process as in laim 1 vvherein theacry1onitril diSSolved in said benzonitTne is separated theleflom byffactiona1 diStillatiol.

Refeences Ced in the e of this patent UNITED STATES PATENTS 2,70Z 300Kener et a1 Feb, 1S 195 Z 736,739 England et aL Feb. 28, 196 Z,738,030KeHer et aL MaT. 13, 19S6 Z,773,088 Mas1an Dec. 4, 19S6 Z,803,641Sandner et al. Aug. 20, 19S7 Z,878 166 Dunn Ma1. 17 19S9

1. A PROCESS FOR THE ELIMINATION OF SUBSTANTIALLY ALL THE NITROGEN AND ASUBSTANTIAL PROPORTION OF THE PROPANE CONTENT FROM AN ACRYLONITRILEREACTOR PRODUCT GAS CONSISTING ESSENTIALLY OF PROPANE, PROPYLENE,ACRYLONITRILE, AND NITROGEN WHICH COMPRISES INTRODUCING AIDPROPANE-PROPYLENEACRYLONITRILE-NITROGEN STREAM NEAR THE BOTTOM OF ARECTIFICATION TOWER MAINTAINED UNDER SUPERATMOSPHERIC PRESSURE,INTRODUCING BENZONITRILE NNEAR THE TOP OF SAID TOWER, PERMITTING THEBENZONITRILE TO CONTACT THE PROPANE-PROPYLENE-ACRYLONITRILE-NITROGENSTREAM IN COUNTERCURRENT RELATIONSHIP, REMOVING A GASEOUS FRACTIONCONTAINING SUBSTANTIALLY ALL OF THE NITROGEN AND ERICHED IN PROPANE, ANDREMOVING A LIQUID FRACTION COMPRISING BENZONITRILE CONTAINING DISSOLVEDTHEREIN ESSENTIALLY ALL OF THE ACRYLONITRILE, THE PROPYLENE, AND THEREMAINING PROPANE.